Recently, in the field of endoscope, a swallowable capsule endoscope has been proposed. The capsule endoscope is provided with an imaging function and a radio communication function. This capsule endoscope has a function of moving in a body cavity, for example, internal organs such as a stomach and a small intestine with peristalsis thereof, during a period after it is swallowed from a mouth of the subject for observation (examination) until it is naturally discharged from the subject, and of sequentially imaging intra-subject images.
While the endoscope is moving in the body cavity, image data imaged in the body by the capsule endoscope is sequentially transmitted to the outside by radio communications, and stored in a memory provided in an external device. If the subject carries a receiving device having the radio communication function and the memory function, the subject swallows the capsule endoscope and then can freely move until the endoscope is discharged. After the capsule endoscope is discharged, a doctor or a nurse can perform diagnosis by displaying the images of the internal organs based on the image data stored in the memory (see, for example, Patent Document 1).
Further, in the conventional capsule endoscope system, one having a mechanism for detecting the position of the capsule endoscope in the body cavity has been proposed. For example, a magnetic field is generated, which has the position dependency regarding strength inside the subject into which the capsule endoscope is introduced, and the position of the capsule endoscope in the subject can be detected based on the magnetic field strength detected by a magnetic field sensor incorporated in the capsule endoscope. In such a capsule endoscope system, a configuration in which a predetermined coil is arranged outside the subject is adopted to generate the magnetic field, and by allowing predetermined electric current to flow to the coil, the magnetic field is generated inside the subject. Since it is difficult to detect the position of the capsule endoscope beforehand, the magnetic field to be generated needs to be generated so that the capsule endoscope has detectable strength in all areas where the capsule endoscope can be present inside the subject. Specifically, in the conventional capsule endoscope system, a magnetic field capable of detecting the capsule endoscope is generated in all the digestive organs from an oral cavity to an anus.
Patent Document 1: Japanese Patent Application Laid-open No. 2003-19111